The present invention relates to radio communication systems. More particularly, and not by way of limitation, the present invention is directed to a front-end architecture and processing method for a receiver in a multi-antenna, multi-band radio.
Cellular telecommunication systems are deployed on multiple frequency bands such as 850 MHz, 900 MHz, 1500 MHz, 1800 MHz, and 1900 MHz. More bands, such as 450 MHz and 700 MHz are likely to become available in parts or all of the world. Radio receivers, such as those utilized in mobile terminals, may operate on more than one band. For each band, there is a receive chain comprising a number of components such as the antenna, low noise amplifier, correlators, combiners, estimators, and the like. Mobile terminals that operate in all or most of these bands must duplicate parts of their receive chain and tune each duplicated part to a specific band.
Some of the receiver components are optimized for a particular band, such as the cellular band at 850 MHz or 900 MHz. Although these are fairly wide bands, a single receive chain can generally be utilized to cover an entire band with good performance. In addition, the same receive chain can be utilized to cover an adjacent or nearly adjacent band with reasonably good performance. For example, a single receive chain designed for the 850 MHz band may work reasonably well for parts or all of the 900 MHz band. While the resulting performance from that receiver would probably not be considered adequate in the 900 MHz band when viewed in isolation, the receiver would still be a useful component of a multi-antenna receiver that processes different signals jointly.
Some bands, however, are widely separated. For example, in the US, operators utilize the 1900 MHz band and the 850 MHz band, while in Europe the 1800 MHz band and the 900 MHz band are utilized. When there are significant differences between the bands, the band-dependent components in a receive chain do not work well in both bands. Certain GSM phones actually have two separate receivers, one for the low band and one for the high band. Depending on the make and model of the phone, the antennas may also be different for each band.
Duplication of receive chains creates problems for the designers of mobile terminals. The duplicated components add to the size, cost, weight, and battery consumption of the terminal. As market requirements continue to push for smaller terminals with additional features, it becomes increasingly important to make efficient use of all of the space within the terminal. The present invention provides a receiver that makes more efficient use of space within the terminal while maintaining good performance over multiple frequency bands.